The present invention is related to an insulation material for use on subsea oil and gas production equipment.
When subsea oil and gas wells are located at depths of 5,000 feet or more, the pipelines and wellhead equipment are exposed to seawater which is just a few degrees above freezing. This same temperature can exist in shallow water at extreme latitudes, such as in the North Sea. During a temporary well shutdown, hot produced fluids within the production equipment become stagnant and are cooled by the surrounding seawater. If the stagnant fluids approach the seawater temperature, hydrates can form in the equipment and block the flow of the fluid.
Thermal insulation is sometimes used around subsea pipelines and wellhead equipment to slow the cooling process and delay hydrate formation until flow can be restored. To perform successfully in this environment, a thermal insulation material must have a low thermal conductivity, maintain acceptable insulating and mechanical properties under hydrostatic compression and long term exposure to seawater, have a low rate of water absorption under high pressure, be economical to install, repair and remove on complex or irregular shapes, cure without cracking or leaking from a mold, be flexible and impact resistant, and have good adhesion to the insulated surfaces.
One method of insulating undersea systems involves the use of pre-cast sections of rigid epoxy-syntactic foam. This material comprises a rigid epoxy resin mixed with a high volumetric proportion of hollow glass or ceramic spheres. Although this material exhibits excellent thermal conductivity, it is very brittle. The installation process, which is laborious and expensive, involves casting the material into sheets which are then cut and shaped piecemeal to match the surface of the subsea equipment. Due to the rigidity and brittleness of this material, it is easily damaged when subjected to sudden impacts or high stress levels. To compound this problem, rigid epoxy-syntactic foams are difficult to repair. Removal or replacement of this material is extremely difficult because the sections are bonded to the surface using adhesives or mechanical fasteners.
An alternative to pre-cast epoxy-syntactic foams is a cast-in-place, rigid epoxy-syntactic, such as Textron TyMar 10K(trademark). Unfortunately, these materials are inherently brittle and exhibit a high exothermic temperature on curing, which causes excessive thermal expansion. This combination of thermal expansion and brittleness results in extensive cracking when the material is cast in large sections. This material also exhibits a high rate of water absorption. Furthermore, when cracking does occur during handling or service, a protective resin coated fiberglass wrap is required to keep the material in place.
Alternate materials include urethane syntactics. However, these materials exhibit a higher rate of water absorption, and are relatively expensive. Also, the typically short curing times of urethane syntactics make them difficult to cast in large or complex sections.
The present invention is a thermal insulation material which comprises a matrix made from a novolac cured polysulfide polymer resin. The preferred resin is a modified version of Thiokol(copyright) FNEC 2515, in which the amount of the tertiary amine in the resin hardener has been reduced to slow the curing reaction and thereby decrease the maximum exothermic temperature generated during curing. The thermal insulation material also comprises a plurality of preferably hollow glass beads contained within the matrix to decrease the exothermic heat generated during curing and also improve the thermal conductivity of the material. In addition, a fumed silica thixotropic material may be added to the thermal insulation material to increase its viscosity.
The thermal insulation material of the present invention exhibits many advantageous properties which make the material particularly beneficial for use on subsea oil and gas production equipment. The matrix material is highly flexible, which makes the insulation material resistant to cracking under thermal or mechanical stress. In addition, the reduced exothermic heat decreases the thermal expansion rate exhibited by the insulation material during curing. Also, because of its flexibility and minimal thermal expansion, the insulation material of the present invention can be cast-in-place in thick sections without cracking. Furthermore, the increased viscosity of the insulation material prevents the mixture from leaking through seams in the mold during application, further improving the cast-in-place performance of the material The insulation material also exhibits a low rate of water absorption, and excellent adhesion to both bare metals and epoxy coatings. Thus, the material as cast exhibits mechanical and thermal properties which are well within acceptable limits for subsea equipment applications. Furthermore, these properties remain within acceptable limits even after prolonged exposure to water at high temperatures and pressures.